Researchers estimate that between 2000 and 2050, the number of older individuals (over the age of 65 years) in the United States will increase 135%, whereas the population under age 65 will increase only 32% (Wiener & Tilly, 2002). The number of individuals living to an advanced age (age 85 and older)—a group likely to need health- and long-term care services—is projected to increase by a staggering 350%. These percentages trans-late to an estimated increase of 47 million individuals age 65 and older (Wiener & Tilly, 2002). An important issue will be to develop strategies to address the health needs of this ever-growing sector of the population.
It is well documented in the literature that cognition significantly declines as people age. This decline includes changes in executive function, fluid intelligence and working memory, inhibitory control and attention, and language processing (see Craik & Salthouse, 2007, for a detailed review). In addition to cognitive declines, there are significant age-related declines in vision and visual processing that influence the health and well-being of an aging population. These declines have been identified as a major factor in the incidence of falls among the elderly (Lord, Smith, & Menant, 2010). In addition, age-related declines in vision have been associated with increased risk of motor-vehicle crashes (Owsley et al., 1998; Owsley, Stalvey, Wells, & Sloane, 1999); in fact, the crash risk for drivers over the age of 75 exceeds that for novice young drivers (Evans, 2004). The types of crashes that occur change with driver age: Compared with younger drivers, older drivers have more collisions with other moving vehicles and less single-vehicle or speed-related crashes (Langford & Koppel, 2006), which suggests that there are specific declines in visual function with age.
Given the health outcomes of age-related declines in vision, an important question is what aspects of vision and visual processing decline with age. A substantial corpus of research (see Owsley, 2011, and Andersen, 2012, for reviews) has shown age-related declines in a vast range of visual functions, including contrast sensitivity. (Richards, 1977), orientation discrimination (Betts, Sekuler, & Bennett, 2007), visual acuity (Sekuler, Owsley, & Hutman, 1982), motion perception (Bennett, Sekuler, & Sekuler, 2007), form perception (Roudaia, Bennett, & Sekuler, 2008), and optic flow (Atchley & Andersen, 1998). While these age-related declines in visual function could be due to optical, retinal, cortical, or pathological changes, there is substantial evidence suggesting a corti-cal locus (Spear, 1993). Specifically, studies have suggested that these changes may be due to decreased cortical inhibition in visual cortex (Schmolesky, Wang, Pu, & Leventhal, 2000).
Of all these age-related declines in vision and visual processing, the decline in contrast sensitivity is one of the most pronounced. Declines in contrast sensitivity significantly affect visual function, including the ability to detect and resolve detail (e.g., Owsley, Sekuler, & Siemsen, 1983), process motion information important for balance (Sundermier, Woollacott, Jensen, & Moore, 1996), and process information when driving (Liutkevic{hacek over ( )}iene, Cebatoriene, Liutkevic{hacek over ( )}iene, Jas{hacek over ( )}inskas, & Zaliu-niene, 2013). Declines in contrast sensitivity have also been found to be related to the likelihood of falls among older adults (Lord, Clark, & Webster, 1991). Contrast-sensitivity declines are most apparent at high spatial frequencies, and while it has been suggested that this decrease in contrast sensitivity is primarily due to optical factors, the decline in contrast sensitivity for moving stimuli may have a significant neural component (Burton, Owsley, & Sloane, 1993).